100+ Free InterNACHI Certified Radon Tester Practice Questions

The EPA action level is 4 pCi/L (148 Bq/m³). Levels at or above this trigger a recommendation to mitigate. The level reflects a balance of feasibility of mitigation and lifetime lung cancer risk; the WHO reference level is lower at 2.7 pCi/L (100 Bq/m³). EPA also recommends considering mitigation between 2 and 4 pCi/L.

Rn-222 has a half-life of 3.82 days and decays by alpha emission to Po-218. The short-lived progeny Po-218 (3.1 minutes) and Po-214 (164 microseconds) are alpha emitters that deposit on lung tissue and account for nearly all of the radiation dose to the lung. Pb-214 and Bi-214 are beta/gamma emitters in the same chain.

Closed-house conditions require keeping all windows closed and external doors closed except for normal entry/exit, and not operating whole-house fans or window air conditioners that bring in outdoor air. They must begin at least 12 hours before a short-term test starts and be maintained throughout the entire test period for tests shorter than one week.

Devices are placed on the lowest livable level (lowest level that is or could be lived in), at least 20 inches above the floor, at least 4 inches from any other object, and away from drafts, exterior walls, windows, doorways, fireplaces, HVAC supply and return registers, and direct sunlight. They should also be at least 3 feet from exterior walls.

Short-term tests run 2 to 90 days; most short-term passive devices (charcoal canisters, electret short-term) and continuous radon monitors are deployed for 2–7 days. Long-term tests run more than 90 days — typically 90 days to one year using alpha-track or long-term electret detectors — and give a better estimate of annual average exposure.

ANSI-AARST MS-QA-2023 requires duplicate measurements (at least 10% of tests), blanks (at least 5% for passive devices), known-exposure spike tests (typically 3 per year), and routine calibration of continuous radon monitors. CRMs must undergo an annual calibration cross-check against a reference standard or chamber.

Real-estate testing under ANSI-AARST MAH-2023 requires tamper-resistance measures (sealed deployment, signed test conditions, two simultaneous detectors or a CRM with hourly logging) because the occupant may have an incentive to influence the result. The test must be on the lowest occupiable level and the device must be sealed and chain-of-custody documented at retrieval before lab submission.